Features of the polymorphic transformations in iron of different purity and zirconium iodide were studied using high-resolution calorimetry methods. It has been suggested that the polymorphic transformations in zirconium, in contrast to the polymorphic transformations in iron, were controlled by two mechanisms: diffusion-free and diffusion. The relationship between them depends on the rate of thermal cycling and the thermal background of zirconium.

С использованием дифференциальной сканирующей калориметрии высокого разрешения исследованы процессы кристаллизации в чистых металлах и в некоторых двухкомпонентных сплавах на их основе. При кристаллизации обнаружены скачки теплового потока по достижению линий ликвидуса. Предполагается, что эти явления связаны с образованием в жидкости большого количества локальных микрообъемов (концентрационных флуктуаций), обогащенных ведущим кристаллизацию компонентом. Их появление предшествует началу процессов спонтанного образования и роста кристаллов новой фазы.

Using differential scanning calorimetry, the regularities of polymorphic α↔β transformation in polycrystalline titanium WТ 1-00 were studied. The values of the activation energy of the α↔β transformation during heating of titanium (760±30 kJ/mol and 1100±100 kJ/mol) were determined, which were dependent on the thermal history of the metal. It is suggested that the recrystallization mechanisms during heating and cooling are controlled by diffusion-free and diffusion mechanisms implemented in overlapping temperature intervals.

Differential scanning calorimetry was used to study the regularities of polymorphic αβ transformation in polycrystalline cobalt. The value of the activation energy of the αβ transformation during heating of cobalt (29050 kJ/mol), enthalpy and entropy, depending on the thermal history of the metal, is determined. It is shown that the mechanisms of recrystallization under heating are closer to the first-order I phase transformations. When cooling under conditions of limited diffusion mobility of cobalt atoms, recrystallization is apparently carried out due to the passage of several diffusion-free mechanisms of phase transformation, implemented in close temperature ranges.

Based on the analysis of differential scanning calorimetry data, the possibility of classifying the observed endothermic or exothermic transformations as phase transformations of the first oder is considered. Two approaches have been implemented. The first is based on the correspondence between the temperatures of the maximum conversion rate and the temperatures of the extrema on the second derivative of the differential scanning calorimetry signal with respect to temperature. In the second approach, the phase transformation is considered as a kind of kinetic reaction of a chemical process with the determination of some parameters included in the kinetic equations. In this case, the order parameter of such reaction n is obtained from the analysis of the differential scanning calorimetry signal shape in the region of phase transformation registration temperatures. Using the example of experiments carried out during thermal cycling of titanium iodide samples, it is shown that both the first and second approaches make it possible to fairly adequately attribute the processes that cause calorimetric effects on the dependences of differential scanning calorimetry to first-order phase transitions. In particular, the obtained results of differential scanning calorimetry during heating and cooling of iodide titanium show that polymorphic transformations in it are realized by various mechanisms depending on the rate of thermal cycling and the thermal history of the metal.